1. Field of the Invention 
The present invention relates to a falling film evaporator of a refrigerant system. More particularly, the present invention relates to a distributor and baffle system that directs the flow of a two-phase refrigerant mixture entering and vapor leaving the evaporator. 
2. Description of Related Art 
The primary components of a refrigeration chiller include a compressor, a condenser, an expansion device and an evaporator. Higher pressure refrigerant gas is delivered from the compressor to the condenser where the refrigerant gas is cooled and condensed to the liquid state. The condensed refrigerant passes from the condenser to and through the expansion device. Passage of the refrigerant through the expansion device causes a pressure drop therein and the further cooling thereof. As a result, the refrigerant delivered from the expansion device to the evaporator is a relatively cool, saturated two-phase mixture. 
The two-phase refrigerant mixture delivered to the evaporator is brought into contact with a tube bundle disposed therein and through which a relatively warmer heat transfer medium, such as water, flows. That medium will have been warmed by heat exchange contact with the heat load which it is the purpose of the refrigeration chiller to cool. Heat exchange contact between the relatively cool refrigerant and the relatively warm heat transfer medium flowing through the tube bundle causes the refrigerant to vaporize and the heat transfer medium to be cooled. The now cooled medium is returned to the heat load to further cool the load while the heated and now vaporized refrigerant is directed out of the evaporator and is drawn into the compressor for recompression and delivery to the condenser in a continuous process.  
More recently, environmental, efficiency and other similar issues and concerns have resulted in a need to re-think evaporator design in refrigeration chillers in view of making such evaporators more efficient from a heat exchange efficiency standpoint and in view of reducing the size of the refrigerant charge needed in such chillers. In that regard, environmental circumstances relating to ozone depletion and environmental warming have taken on significant importance in the past several years. Those issues and the ramifications thereof have driven both a need to reduce the amount and change the nature of the refrigerant used in refrigeration chillers. 
So-called falling film evaporators, which are known in the industry, have for some time been identified as appropriate for use in refrigeration chillers to address efficiency, environmental and other issues and concerns in the nature of those referred to above. While the use and application of evaporators of a falling film design in refrigeration chillers is theoretically beneficial, their design, manufacture and incorporation into chiller systems has proven challenging, particularly with respect to the need to uniformly distribute refrigerant across the tube bundles therein. Uniform distribution of the refrigerant delivered into such evaporators in a refrigeration chiller application is critical to the efficient operation of both the evaporator and the chiller as a whole. Achieving the uniform distribution of refrigerant is also a determining factor in the success and efficiency of the process by which oil, which migrates into the evaporator, is returned to the chiller's compressor. The efficiency of the process by which oil is returned from a chiller's evaporator affects both the quantity of oil that must be available within the chiller and chiller efficiency. U.S. Pat. No. 5,761,914, assigned to the assignee of the present invention, may be referred to in that regard.  
Exemplary of the current use of falling film evaporators in refrigeration chillers is the so-called RTHC chiller manufactured by the assignee of the present invention. In addition to the '914 patent referred to above, reference may be had to U.S. Pat. Nos. 5,645,124; 5,638,691 and 5,588,596, likewise assigned to the assignee of the present invention and all of which derive from a single U.S. patent application, for their description of early efforts as they relate to the design of falling film evaporators for use in refrigeration chillers and refrigerant distribution systems therefor. Reference may also be had to U.S. Pat. No. 5,561,987, likewise assigned to the assignee of the present invention, which similarly relates to a chiller and chiller system that makes use of a falling film evaporator. 
In the RTHC chiller, the refrigerant delivered to the falling film evaporator is not a two-phase mixture but is in the liquid state only. As will be apparent to those skilled in the art, uniform distribution of liquid-only refrigerant is much more easily achieved than is distribution of a two-phase refrigerant mixture. The delivery of liquid-only refrigerant for distribution over the tube bundle in the falling film evaporator in the RTHC chiller, while making uniform refrigerant distribution easier to achieve, is achieved at the cost and expense of needing to incorporate a separate vapor-liquid separator component in the chiller upstream of the evaporator's refrigerant distributor. The separate vapor-liquid separator component in the RTHC chiller adds significant expense thereto, in the form of material and chiller fabrication costs, such vapor-liquid separator component being a so-called ASME pressure vessel, which is relatively expensive to fabricate and incorporate into a chiller system. 
Recently developed chillers have flow distribution systems that can effectively direct the flow of a two-phase refrigerant mixture through a falling film evaporator. Examples of such chillers are disclosed in U.S. Pat. Nos. 6,167,713 and 6,293,112, which are assigned to the assignee of  the present invention and are specifically incorporated by reference herein. To evenly distribute two-phase refrigerant across the full length and width of a tube bundle, the chillers of the '713 and '112 patents have a flow distributor that includes a diamond-shaped suction inlet duct that feeds a stack of perforated plates. One of the plates has a series of diamond-shaped passages that promotes lateral flow for even distribution of refrigerant over the width of the tube bundle. The inlet duct is also preferably a diamond-shape to evenly distribute the refrigerant along the length of the tube bundle. Although such a distributor is quite effective, it can be difficult and expensive to produce. Assembling and attaching the multiple plates can involve extensive processing in the form of welding or other joining operations and can add a significant amount of weight to the distributor. 
In some cases, baffles are installed between the evaporator outlet and the area where the refrigerant is vaporized by the tube bundle. The baffles can help separate the liquid and gas components of the two-phase refrigerant mixture so that the portion of refrigerant returned to the suction side of the compressor is almost entirely gaseous refrigerant. The liquid part, which may include some oil for compressor lubrication, can then remain in the evaporator until the refrigerant is vaporized. The oil, which remains as a liquid, can be pumped back to the compressor or returned by some other means. 
Examples of evaporator baffle systems are disclosed in UK Patent Application GB 2 231 133 and in U.S. Pat. Nos. 2,059,725; 2,384,413; 3,326,280 and 5,561,987. A drawback of many baffle systems is their failure to take into account a refrigerant's uneven flow velocity which may vary along the length of the evaporator shell. Uneven flow velocities are particularly prevalent when the evaporator shell has its outlet  at one end of the shell rather than being centrally located. Gaseous refrigerant flowing at higher velocities may have a greater tendency to carry liquid refrigerant out of the evaporator, so uneven flow rates can be detrimental. 
Consequently, a need exists for an economical flow distributor and baffle system that can evenly distribute and separate a two-phase refrigerant mixture flowing through a falling film evaporator. 